html, body {
  height: 100%;
  width: 100%;
  padding: 0;
  margin: 0;
}

body {
  display: flex;
  flex-direction: column;
}

header {
  background-color: aqua;
}

footer {
  background-color: brown;
}

div.content {
  display: flex;
  flex-direction: row;
  flex-grow: 1;
}

div.content > div {
  height: 100%;
}

div.content > .left-menu {
  width: 196px;
  background-color: aquamarine;
}

div.content > .edit-area {
  flex-grow: 1;
  background-color: blueviolet;
}

div.content > .index {
  background-color: yellowgreen;
}